This invention relates to a process for preparing halopropyldimethylchlorosilanes which are useful as intermediates for the synthesis of various silane coupling agents and as modifiers for silicone fluid.
Halopropylchlorosilane compounds are used as intermediates for the synthesis of various silane coupling agents and as modifiers for silicone fluid. These compounds are generally synthesized by reacting allyl halides with hydrogenchlorosilane compounds such as trichlorosilane, methyldichlorosilane and dimethylchlorosilane. In the reaction, platinum and rhodium-containing compounds are used as the catalyst.
The process of preparing halopropylchlorosilane compounds using platinum-containing compounds is disclosed, for example, in U.S. Pat. Nos. 2,823,218, 3,814,730, 3,715,334, 3,516,946, 3,474,123, 3,419,593, 3,220,922, 3,188,299, 3,178,464, and 3,159,601. The process using rhodium-containing compounds is disclosed, for example, in U.S. Pat. Nos. 3,296,291 and 3,564,266. Most of these processes use trichlorosilane and methyldichlorosilane as the hydrogenchlorosilane compound.
The use of trichlorosilane and methyldichlorosilane as the hydrogenchlorosilane compound is described in many patents as noted above. However, the use of dimethylchlorosilane is described in few patents because of low selectivity of reaction, although the end products, halopropyldimethylchlorosilane compounds are useful as intermediates for the synthesis of various silane coupling agents and as modifiers for silicone fluid. The only known process is Japanese Patent No. 2938731 directed to the preparation of a halopropyldimethylchlorosilane compound using an iridium complex. This process, however, suffers from the problem that a large amount of the expensive iridium complex must be used as the catalyst, and is thus not regarded as advantageous in practicing on an industrial scale.
An object of the invention is to provide a simple process for preparing halopropyldimethylchlorosilanes on an industrial scale.
The invention pertains to a process for preparing a halopropyldimethylchlorosilane of the following general formula (1):
XCH2CH2CH2Si(CH3)2Clxe2x80x83xe2x80x83(1)
wherein X is chlorine, bromine or iodine, by reacting dimethylchlorosilane with an allyl halide of the following general formula (2):
XCH2CHxe2x95x90CH2xe2x80x83xe2x80x83(2)
wherein X is as defined above in the presence of an iridium catalyst. Quite unexpectedly, the inventor has found that deactivation of the iridium catalyst during reaction is suppressed by adding an internal olefin compound of the following general formula (3) to the reaction system. 
Herein R1 and R2 each are a monovalent hydrocarbon group having 1 to 10 carbon atoms, or R1 and R2 may together form a ring, R3 and R4 each are hydrogen or a monovalent hydrocarbon group having 1 to 10 carbon atoms. Even when the amount of the iridium catalyst used is reduced, the halopropyl-dimethylchlorosilane is produced in high yields.
The invention provides a process for preparing a halopropyldimethylchlorosilane of the general formula (1):
XCH2CH2CH2Si(CH3)2Clxe2x80x83xe2x80x83(1)
reacting dimethylchlorosilane with an allyl halide of the general formula (2):
XCH2CHxe2x95x90CH2xe2x80x83xe2x80x83(2)
in the presence of an iridium catalyst, characterized in that the reaction is effected in the presence of a compound of the general formula (3): 
Herein, X and R1 to R4 are as defined above.
The starting reactant to be reacted with dimethyl-chlorosilane is an allyl halide of the general formula (2):
XCH2CHxe2x95x90CH2xe2x80x83xe2x80x83(2)
wherein X is chlorine, bromine or iodine. Specifically, the allyl halides are allyl chloride, allyl bromide and allyl iodide. The amount of the allyl halide used is not critical although it is preferred to use 0.5 to 2.0 mol, especially 0.9 to 1.2 mol of allyl halide per mol of dimethylchlorosilane.
The iridium catalyst used herein encompasses iridium salts and iridium complexes. Exemplary iridium salts are iridium trichloride, iridium tetrachloride, chloroiridic acid, sodium chloroiridate and potassium chloroiridate. The iridium complexes include those represented by the following general formula (4):
[Ir(R)Y]2xe2x80x83xe2x80x83(4)
wherein R is a diene compound and Y is chlorine, bromine or iodine. Illustrative examples of the iridium complexes of formula (4) include di-xcexc-chlorobis(xcexc-1,5-hexadiene)diiridium, di-xcexc-bromobis(xcexc-1,5-hexadiene)diiridium, di-xcexc-iodobis(xcexc-1,5-hexadiene)diiridium, di-xcexc-chlorobis(xcexc-1,5cyclooctadiene)diiridium, di-xcexc-bromobis(xcexc-1,5-cyclooctadiene)diiridium, di-xcexc-iodobis(xcexc-1,5-cyclooctadiene)diiridium, di-xcexc-chlorobis(xcexc-2,5-norbornadiene)diiridium, di-xcexc-bromobis(xcexc-2,5-norbornadiene)diiridium, and di-xcexc-iodobis(xcexc-2,5,-norbornadiene)diiridium.
No particular limit is imposed on the blending ratio of the iridium catalyst although it is preferred to use the iridium catalyst in such amounts as to give 0.000001 to 0.01 mol, especially 0.00001 to 0.001 mol of iridium atom per mol of dimethylchlorosilane. Less than 0.000001 mol of the catalyst may fail to exert catalytic effects whereas more than 0.01 mol of the catalyst may not provide reaction promoting effects corresponding to the increment of the catalyst.
According to the invention, the reaction of dimethylchlorosilane with the allyl halide of formula (2) is carried out in the presence of not only the iridium catalyst, but also an internal olefin compound of the formula (3). 
Herein R1 and R2 each are a monovalent hydrocarbon group having 1 to 10 carbon atoms, or R1 and R2, taken together, may form a ring. R3 and R4 each are hydrogen or a monovalent hydrocarbon group having 1 to 10 carbon atoms. Illustrative examples of the compound of formula (3) include 2-hexene, 3-hexene, 2-heptene, 2-octene, 4-octene, 2-decene, 5-decene, cyclopentene, cyclohexene, 2-norbornene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, 4-vinyl-1-cyclohexene, 1,5-cyclooctadiene, 2,5-norbornadiene, 5-vinyl-2-norbornene, and limonene. From the reactivity and catalyst stability standpoints, 1,5-cyclooctadiene is most preferred.
No particular limit is imposed on the amount of the compound of formula (3) used although it is preferred to use 0.5 to 10,000 mol, especially 1 to 1,000 mol of the compound per mol of iridium atom in the iridium catalyst. Less than 0.5 mol of the compound may fail to exert the desired effects whereas more than 10,000 mol of the compound may fail to provide effects corresponding to that amount and cause more by-products to form, resulting in reduced yield and purity.
The reaction will proceed in a solventless system although a solvent is used if desired. Useful solvents include hydrocarbon solvents such as pentane, hexane, cyclohexane, heptane, octane, isooctane, benzene, toluene, and xylene; ether solvents such as diethyl ether, tetrahydrofuran, and dioxane; ester solvents such as ethyl acetate and butyl acetate; aprotic polar solvents such as acetonitrile; and chlorinated hydrocarbon solvents such as dichloromethane and chloroform, which may be used alone or in admixture of two or more.
The reaction temperature is not critical. A temperature in the range of about 0xc2x0 C. to about 200xc2x0 C., especially about 10xc2x0 C. to about 100xc2x0 C. is preferred when reaction is effected under atmospheric pressure or under pressure. The reaction time is usually from about 1 hour to about 10 hours.
According to the invention, the above-described reaction yields a halopropyldimethylchlorosilane of the general formula (1):
XCH2CH2CH2Si(CH3)2Clxe2x80x83xe2x80x83(1)
wherein X is chlorine, bromine or iodine. Specifically, the silanes are 3-chloropropyldimethylchlorosilane, 3-bromopropyldimethylchlorosilane, and 3-iodopropyldimethyl-chlorosilane.